In the past few years, the general public has become increasingly apprehensive of the impact man-made waste has on the environment. Hence there is a growing interest in developing novel biodegradable (and preferably compostable) plastics from renewable resources.
One particularly interesting candidate for this task is poly(hydroxy carboxylic acid), in particular poly(lactic acid) (PLA), now commercially available on a relatively large scale. The lactic acid is obtained from plants such as corn and sugar-cane or other sugar- or starch-producing plants. Not only is PLA obtainable from renewable materials, it is also industrially compostable. For these reasons, there is significant interest in using PLA as a substitute in applications, where petroleum-based thermoplastics have conventionally been used.
Unfortunately, PLA used on its own does not have the same advantageous properties as conventional plastics do. In particular PLA has performance problems related to heat resistance, brittleness and limited flexibility, resulting in poor mechanical strength. On the other hand, polyolefins, such as polypropylene, have much better mechanical properties. It has been attempted to combine these properties by blending PLA with polypropylene to obtain a resin that is at least partially obtainable from renewable resources, but still has acceptable mechanical properties. However, it is known that blending PLA with conventional polypropylenes such as Ziegler-Natta-catalysed polypropylenes provides heterogeneous resin blends, due to the differences in polarity and molecular weight distribution of the two components. In the past, compatibilising agents were used to increase the homogeneity of the blends. However, this requires an additional industrial step, as well as specific conditions during extrusion. Furthermore, the addition of compatibilising agents is expensive and changes the properties of the desired product. Thus both the compatibilising agent and the by-products change the properties of the desired end product, be it a film, fibre or moulded object.
JP 2005307128 A discloses a blend of PLA and polypropylene using a compatibilising agent, in this case a polypropylene grafted with a vinyl carboxylic acid, vinyl anhydride or another vinyl derivative.
JP 2006348060 A also describes a thermoplastic resin comprising from 20-90 wt % PLA and 10-80 wt % polypropylene with 1-20 pts.wt of compatibiliser.
EP 1 777 263 A also teaches mixing polyolefins with PLA by using a compatibiliser, wherein the compatibiliser is a hydrogenated, diene-based polymer containing at least one functional group selected from carboxyl group, acid anhydride group, epoxy group, (meth)acryl group, amino group, alkoxysilyl group, hydroxyl group, isocyanate group and oxazoline group.
US 2005/0192405 A discloses a polymer blend of PLA and polyolefins. The two components are mixed by including a polyalkylacrylic ester and/or a polyvinyl ester, as well as a block copolymer of a polyalkylacrylic ester and a polyolefin and/or a block copolymer of a polyvinyl ester and a polyolefin, which act as compatibilising agents.
It is hence an object of the invention to develop a polypropylene-based resin, that is at least partially obtainable from renewable resources and has better or at least similar mechanical properties than hitherto known blends of polypropylene with resins obtainable from renewable resources.
It is also an object of the invention to develop a resin that is at least partially obtainable from renewable resources and has improved mechanical properties in comparison with poly(hydroxy carboxylic acid)s.
Additionally, it is an object of the invention to develop a resin that is at least partially obtainable from renewable resources and has similar mechanical properties to polypropylene.
It is hence an object of the invention to develop a resin that has better gas barrier properties than polypropylene.
It is also an object of the invention to develop a resin with better surface tension properties than polypropylene.
Furthermore, it is an object of the invention to blend polypropylene with poly(hydroxy carboxylic acid)s without having to use compatibilising agents to obtain homogeneous blends.
It is also an object of the invention to find a resin at least partially obtainable from renewable resources that can be used in film, fibre, thermoforming, blow moulding, injection stretch blow moulding, extrusion blow moulding or rotational moulding applications.
At least one of the above objects is achieved with the implementation of the current invention.